When a load on an Alternating Current (AC) power source is not a linear load (i.e., the load is a non-linear load) the current being drawn from the AC power source may be out of phase with the voltage of the AC power source. A purely resistive load is a linear load. A load having an energy storage component (such as an inductance or a capacitance) may be a non-linear load. A load that draws power irregularly over the course of a cycle of the AC power source, such as a rectifier or a Switch Mode Power Supply (SMPS), may be a non-linear load.
When the current being drawn by a non-linear load from the AC power source is out of phase with the voltage of the AC power source, the current being drawn from the AC power source will be higher, on average, than it would be if the current and voltage were in phase. This can cause power to be wasted and damage to occur in the AC power source.
The degree to which the current drawn by a load from the AC power source is in phase with the voltage of the AC power source may be expressed as the Power Factor (PF) of the load. An ideal linear load has a PF of 1, and non-linear loads have a PF less than one.
A PFC circuit may be provided between an AC power source and a load. The PFC circuit operates to present a PF close to 1 (e.g., 0.98) to the AC power source by keeping the phase of current drawn from the AC power source close to the phase of the voltage of the AC power supply, even when the phase of the current drawn by the load is out of phase or irregular.
It is desirable for a PFC circuit to maintain a high level of efficiency as the current drawn by the load varies and as the voltage of the AC power source varies. It is desirable for a PFC circuit to not subject the AC power source to glitches or other distortions in the current drawn from the AC power source.